Polysaccharide oxidized products

ABSTRACT

A novel oxidized non cellulosic polysaccharide which is useful as a wet strength additive in paper making is described. The starting material is preferably a naturally occurring polysaccharide gum or a seaweed extractive, and these materials are oxidized, without degradation of the ring structure of the hexose units, with an acid-dichromate system so that at least some of the initial primary alcohol groups at the C6 positions are oxidized to aldehyde groups.

United States Patent Vemuri [S4] POLYSACCHARIDE OXIDIZED PRODUCTS [72] Inventor: Krishna P. Vemuri, Appleton, Wis.

[73] Assignee: Abitibi Paper Company, Ltd., To-

ronto, Ontario, Canada [22] Filed: June 5, 1969 [2l] Appl. No.: 830,664 [30] Foreign Application Priority Data Sept. 30, 1968 Canada ..03l ,235

[52] U.S. Cl. ..260/209 R, 162/178 [5 I] Int. Cl "Co k 47/18 [5 8] Field Of Search 162/ 178; 260/209 R [5 6] References Cited I UNITED STATES PATENTS Jordan ..260/209 R [4 1 Sept. 12, 1972 Germino ..260/209 R Farthouat et al 260/209 R Primary Examiner-Lewis Gotts Assistant Examiner-Johnny R. Brown Attorney-Stevens, Davis, Miller & Mosher [5 7] ABSTRACT 3 Claims, 1 Drawing Figure 1 POLYSACCHARIDEOXIDIZED PRODUCTS This application relates to an additive to promote wet strength in paper making and aprocess to-produce the additive. More particularly, the invention-relates to dehyde groups or with labile side chains linked to the' C positions of the main chain which can be easily detached by a suitable reaction such as hydrolysis thereby rendering the C alcohol groups of. the main chain accessible to oxidation and increasing the total number of such C, aldehyde groups.

Many additive systems have been used to increase the wet strength of paper, including those based on synthetic resins. The prior art systems also include the use of periodate oxidized galactomannan gums, as described in U.S. Pat. No. 3,205,125 issued Sept. 5, 1965 to Opie et al., U.S. Pat. No. 3,228,928 issued Jan. 11, 1966 to Opie et al., U.S. Pat. No. 3,236,832 issued Feb. 22, 1966 to Opie et al. and U.S. Pat. No. 3,239,500 issued Mar. 8, 1966 to Keen et a]. The products of the periodate oxidation of the gums have a dialdehyde structure arising form ring opening and oxidation of a substantial number of the anhydrogalactose units. Typical of these gums is guar gum (galactomannan gum):

CHzOH H CH2 CHaOH 6 oH 5 4 H 1 0 OH 11 l I 11 3\| H which may be periodate oxidized to a. compound hav- 5 ing the structure:

where A is and nis an integer greater than I. It will be noted that the ring structure is broken, and'this is expensive to achieve.

Germino in U.S. Pat. No. 3,297,604 issued Jan. 10, 1967 discloses a method to enhance the wet strength of paper by incorporating into apulp an enzymatically oxidized polymer possessing the galactose configuration at the C position and oxidized at the C position to produce a galacto hexoaldose without ring opening. Typical of the products envisaged is an oxidized guar gum having the following formula:

- H2 H, OH

v g lI-C=O I 11 As this isan enzyme reaction only galactose containing polymers can be oxidized by this process and it will be appreciated, therefore, the oxidation is restricted to a limited group of compounds. Under special'circumstances, depending on the type of pump employed, the process conditions, the type of wood and many other factors, an improvement in the wet strength properties up to about percent can be achieved, but more usually only a slight improvement can be-measured. It is believed that the increase in wet strength can. be attributed, at least in part, to the presence of the aldehyde groups at the galactose C positions and, therefore major improvements in wet strength properties are not possible with the enzymatically oxidized additives produced by Germino.

it. is, therefore, an object of the present invention to provide a novel composition resulting from the chemical oxidation of a non-cellulosic polysaccharide containing at least one form of hexose unit in which the sugar residues in the main chain are linked by glycosidic -/3(l 4)linkages.

A more specific object is to provide a novel non-cellulosic polysaccharide built up of hexose units at least some of whose primary alcohol groups at the C posi- 0 tions, either present in the starting material or liberated by a suitable reaction, have been oxidized to aldehyde groups without simultaneous ring opening of the modified hexose unit.

By another object of the invention there is provided a method of preparing the novel oxidized polysaccharide by oxidation of the starting materials with a dichromate-acid system.

Another object of the invention is to improve the wet strength characteristics of paper without inhibiting the repulping properties by adding the novel compound to a pulp.

The polysaccharide compounds suitable as starting materials in the present invention include the polysaccharide gums such as the galactomannan gums exemplified by guar gum, locust bean gum and damson gum, the glucose-galactose-xylose gums exemplified by gum tamarind and the seaweed extractives exemplified by laminaran, and whose building units are predominantly hexoses preferably, but not essentially of the galactose, mannose or glucose types. By the method of the present invention, these starting materials may be oxidized at the C positions to produce initially predominantly C aldehyde groups without simultaneous ring opening of the modified hexose units. The oxidation process simultaneously produces some C C keto groups while by further reaction a portion of the C aldehyde groups is converted to carboxyl groups which do not contribute to the wet strength improvement desired. In a preferred embodiment, therefore the C carboxyl group formation is suppressed as far as possible by careful selection and control of the oxidation system.

It has been found, for example in a preferred embodiment, that guar gum (Formula (1)) may be oxidized at room temperature in an aqueous solution of potassium dichromate and oxalic acid to produce a modified gum having the structure:

where X is H-C O and may undergo further oxidation to COOH, Y is selected from the group consisting of hydroxyl and the oxygen of a keto, and n is an integer greater than 1.

It will, of course, be appreciated by those skilled in the art that formation of keto groups at the C and C positions causes appropriate elimination of hydrogen atoms. As noted above, the carboxyl and keto groups do not effect a significant increase in wet strength properties and therefore their formation should be limited. It is an inherent property of the oxidation system that at least some carboxyl groups will be formed but the formation should be minimized. When the hexoaldose containing gum of Formula (2) was treated with hydroxylamine hydrochloride to successively convert the C aldehyde groups to oximes, it was found that the wet strength enhancement in paper due to the resulting material behaved as a sole function of the C aldehyde content of the polymer.

This is more clearly shown in the drawing which is a graph of aldehyde content versus wet strength for oxidized locust bean gum with varying contents of aldehyde and carboxyl groups.

These results will be discussed in more detail hereinafter and it will be seen that reduction in aldehyde content and inclusion of carboxyl groups is detrimental to wet strength. It is, therefore, preferred that the oxidized gum shall have as high a concentration of -CHO groups and as low a concentration of COOH groups as possible for maximum enhancement of wet strength properties. Although the C aldehyde groups exert a predominant role in promoting wet strength, the mechanism by which they act is not fully understood. Without wishing to be bound by this explanation, it is believed that the C aldehyde groups form hemiacetal bonds with the OH groups of cellulose which are stronger and hydrolyze more slowly in water than the regular hydrogen bonds in paper.

The novel compounds of the present invention may be prepared by oxidizing the hexose containing polymers in an aqueous dichromate-acid solution for varying times, preferably at room temperature. The dichromate may be any suitable aqueous soluble dichromate such as potassium dichromate, sodium dichromate or ammonium dichromate and the acid is preferably selected from the group consisting of polycarboxylic acids, such as oxalic, citric and tartaric acids; although however, mineral acids such as sulphuric acid may be used. Oxalic acid is the most preferred acid. The molar ratio of dichromate to acid should be in the range 1:10 to 1:3 and preferably about 1:6. After the reaction the oxidized gum may be isolated and stored as an aqueous slurry at room temperature, or preferably at about 5C. until required. Alternatively, the oxidized gum may be isolated and dried at a suitable temperature for storage as a powder. By a further alternative, the reaction mixture per se can be added to a pulp to develop wet strength.

The novel oxidized gums are effective in developing wet strength when added to bleached or unbleached mechanical, semi-chemical and chemical pulps, in an amount which varies from about 0.5 percent by weight of dry pulp up to about 5 percent by weight of dry pulp depending on the end use of the paper. Below 0.5 percent by weight, there is little significant increase in strength and above about 5 percent there is insufficient increase in wet strength to justify the additional cost of the additive. The appropriate amount of modified gum may be boiled in water or aqueous sodium bisulphite for a few minutes and disintegrated by mechanical means to place it in suitable form for addition to the pulp. The pH of the pulp may vary from pl-l3 to pH7 during the paper making process and a retention aid such as paper makers alum is beneficial in obtaining maximum effect from the wet strength additive. Papers made from the pulp containing the additive develop wet strength during the normal drying process or even at room temperature.

The invention will be more clearly understood by reference to the following examples of the novel compositions and methods of use.

EXAMPLE l Thirty grams of locust bean gum powder was oxidized in an aqueous solution of 0.05N potassium dichromate and 0.1N oxalic acid at a consistency of 3 percent for 2 hours at room temperature. After reaction the oxidized gum was isolated from the reaction mixture and washed thoroughly with distilled water. The pH of the reaction mixture varied from 1.6 to 2.7 during the oxidation and the oxidized gum had an aldehyde content of 18.9 m moles/ g. and a carboxyl content of 17.7 m moles/100 g. The oxidized gum at 0.5 percent concentration had a viscosity of 4.5 cps. in comparison with 24.l cps. of the unoxidized gum as measured by an Ostwald Viscometer at 25C.

EXAMPLE 2 Locust bean gum was oxidized under identical conditions as in Example 1 but for the pH of the reaction mixture which was maintained constant at 1.6 by adding 0.lN oxalic acid with the help of a Beckman automatic titrator. The oxidized gum had an aldehyde content of 26.6 m moles/100g. and a carboxyl content of 27.8 m moles/100g.

EXAMPLE 3 tent of 9.1 m-moles/ 100 g. and a carboxyl content of 10.0 m-moles/ 100g.

EXAMPLE 4 Locust bean gum was oxidized as in Example 1 and 0.168 gof it was addedto 8.4 g. of newsprint stock, consisting of 75 percent groundwood (black spruce) and 25 percent ARBISO (Trademark for a bisulphite pulp) black spruce pulp, together with 0.21 g. alum on an dry basis as a retention aid; Standard TAPPI handsheets were formed and tested according to standard TAPPI methods. The sheets'had 175 percent increase in wet strength and percent increase in dry strength over the control sample.

The comparatively small increase in wet strength achieved in this example may be explained, at least in part, by the fact that groundwood contains a large proportion of lignin in addition to cellulose and the wet strength additive is effective only on the cellulosic portion. Bleached chemical pulps, which are largely cellulosic with only minor amounts of lignin show much higher wet strengths with the additive.

EXAMPLE 5 Six grams of bleached bisulphite pulp (yield ca. 50 percent) beaten to a freeness of 360 c.s.f. was treated with 0.12 g. oxidized locust bean gum (as prepared in Example 1) at a pulp consistency of 1.5 percent. Standard TAPPI handsheets were made at pH 7.3 and pH 4.4 (pH established with H 304) and then tested according to the standard methods. A set of untreated control sheets were made by identical methods at pH 7.3. The results were as follows:

Tensile Strength (No./l5 mm width) pH in the Dry Wet sheet mould Control 11.8 0.5 7.3 Pulp with 2% oxidized locust bean gum 15.7 2.5 7.3 Pulp with 2% oxidized locust bean gum 15.8 2.9 4.4

EXAMPLE 6 Locust bean gum was oxidized as in Example 1 and ,the whole reacted oxidation mixture was added to an unbleached kraft pulp and then beaten in a Valley beater. The results showed that with a 2 percent addition of the oxidized gum 30 minutes beating developed wet and dry strength properties beyond those obtained with untreated pulp or pulp containing 2 percent unoxidized gum.

EXAMPLE 7 The procedure of Example 4 was repeated using percent bleached kraft pulp. The handsheets had 440 percent increase in wet strength and 29 percent increase in dry strength over the control sample.

EXAMPLE 8 A 1 percent solution of the oxidized locust bean gum (as prepared in Example 1) was sprayed onto an offset newsprint web and subsequently calendered whereby the amount of lint was reduced to about one half in comparison with the control web. It will be appreciated that in the offset printing process the paper is in contact with water and hence linting is an important factor. This is in distinction to the letterpress printing process where the paper is maintained dry and hence linting is not a problem.

EXAMPLE 9 The procedure of Example 1 was repeated except that ammonium dichromate was used in place of potassium dichromate. Bleached kraft pulp was treated with 2 percent of the oxidized gum on a dry basis and then handsheets were made and tested according to standard procedures. The handsheets had 380 percent increase in wet strength and 35 percent increase in dry strength over the control sample.

EXAMPLE 10 The procedure of Example 1 was repeated except that sodium dichromate was used in place of potassium dichromate. Bleached kraft pulp was treated with 2 percent of the oxidized gum on a dry basis and then handsheets were formed and tested according to standard methods. The sheets had 360 percent increase in wet strength and 34 percent increase in dry strength over the control sample.

EXAMPLE 1 1 The procedure of Example 1 was repeated with citric acid. Bleached kraft pulp was treated with 2 percent of the oxidized gum on a dry basis and then handsheets were formed and tested according to standard methods. The sheets had 130 percent increase in wet strength and 10 percent increase in dry strength over the control sample.

EXAMPLE 12 The procedure of Example 1 was repeated with tartaric acid in place of oxalic acid. Bleached kraft pulp was treated with 2 percent of the oxidized gum on a dry basis. The handsheets had percent increase in wet strength and negligible increase over the control sample.

EXAMPLE 13 The procedure of Example 1 was repeated using sulphuric acid in place of oxalic acid. Bleached AR- BISO (Trademark for a bisulphite pulp) pulp was treated with 2 percent of the oxidized gum on a dry basis. The handsheets had 120 percent increase in wet strength and 19 percent increase in dry strength over the control sample.

EXAMPLE 14 The procedure of Example 1 was repeated with guar gum instead of locust bean gum. Bleached kraft pulp was treated with 2 percent of the oxidized guar gum and handsheets were formed and tested according to standard methods. The sheets had 330 percent increase in wet strength and 22 percent increase in dry strength over the control sample.

EXAMPLE The procedure of Example 1 was repeated with gum tamarind instead of locust bean gum. Bleached kraft pulp was treated with 2 percent of the oxidized gum tamarind and handsheets were made and tested according to standard procedures. The sheets had 270 percent increase in wet strength and 5 percent increase in dry strength over the control sample.

EXAMPLE 16 The procedure of Example 1 was repeated with gum tamarind which was pre-hydrolyzed by 0.1N oxalic acid for 2 hours at room temperature. Bleached kraft pulp was treated with 2 percent of the pre-hydrolyzed, oxidized gum tamarind in presence of 2 percent of alum on dry basis. The handsheets had 400 percent increase in wet strength and 4 percent increase in dry strength over the control sample.

These examples clearly show that the additive is effective to increase the wet strength in paper made from many kinds of pulp and furthermore that the increase in strength is related to the amount of C aldehyde available. It will be noted in Example 13 that sulphuric acid treated gum is not as effective as the preferred oxalic acid treated gum as a wet strength additive, although a substantial increase in wet strength is achieved. It will also be noted in Examples 1, 2 and 3 that the preferred dichromate-oxalic acid system tends to convert about 50 percent of the C aldehyde groups initially formed to carboxyl groups with the result that there is an approximately 1 to 1 molar ratio of aldehyde to carboxyl groups.

In order to distinguish the present invention even more clearly from the prior art and in particular US. Pat. No. 3,297,604, a test was conducted on a similar pulp to that employed in Example 7 using an enzymatically oxidized locust bean gum.

EXAMPLE 17 30 g. of locust bean gum was added to 2 liters of distilled water containing 30 g. of disodium phosphate and 18 g. of monosodium phosphate. 11 mg. of galactose oxidase (which corresponds to 55 units) was added and a reaction was maintained for 24 hours at room temperature under constant agitation and in the presence of atmospheric oxygen. The resultant product was analyzed and found to contain 0.785 percent aldehyde which corresponds to 27.15 m moles/100 g. gum and also to contain 17.5 m moles/100 g. gum of carboxylic groups. It will be observed that the ratio of Cl-lOzCOOH is well in excess of 1:1. On the basis of the results achieved with the product of the present invention it would be predicted that with a ratio of 27.15 :17.5 the wet strength of a 100 percent bleached kraft pulp would be increased from 0.5 lbs. (control sample of Examples 5 and 7) to about 4.0 lbs.

2 percent of the oxidized gum was therefore mixed with percent bleached kraft pulp to which 2 percent alum was added. Standard TAPPI handsheets were prepared as in the previous examples and the wet strength was determined. The wet strength was found to be only 2.3 lbs. which signifies an increase of only 360 percent whereas the product of the present invention improved the wet strength 440 percent on a similar pulp, as shown in Example 7. More importantly the ratio of aldehyde to carboxylic groups in this example is so high that a much higher wet strength should have been obtained.

To demonstrate the effect of carboxyl groups and the ratio of aldehyde/carboxyl on wet strength, a series of tests were performed. Locust bean gum was oxidized under varying conditions with a dichromate-oxalic acid system as follows:

a. Gum A treated with 0.2 N K Cr O and 0.4 N oxalic acid at room temperature for 2 hours at consistency of 3 percent as in Example 1 to produce a modified gum containing 32 millimoles CH0 and 40 millimoles COOl-l per 100 g. of gum.

. Gum B treated exactly as the gum in Example 2 to produce a modified gum containing 27 millimoles CH0 and 27.8 mollimoles of COOl-l per 100 g. of gum.

c. Gum C treated exactly as the gum in Example l to produce a modified gum containing 19 millimoles CH0 and 17.7 millimoles of COOH per 100 g. of

gum.

. Gum D treated exactly as the gum in Example 3 to produce a modified gum containing 8.5 millimoles CH0 and 10.0 millimoles COOl-l per 100 g. of

gum.

2 percent of these modified gums were incorporated into handsheets prepared from bleached kraft pulp. The conventional wet strength test was applied to the sheets and the four points A, B, C and D on graph were plotted, showing wet strengths of 1.8, 2.5, 3.0 and 2.9 lbs./4 inches X 15mm respectively. The wet strength of a control pulp containing no additive was also determined and the result plotted.

Each modified gum A, B, C and D was reacted independently with varying amounts of hydroxylamine hydrochloride to block, to varying degrees, the aldehyde groups while not further modifying the COOH content. For example, the Gum C was divided into three fractions, each fraction was adjusted to pH 4.7 and reacted with hydroxylamine hydrochloride, as indicated in Table l, for 20 hours at room temperature. The resultant gums were then incorporated into batches of the same bleached kraft pulps previously employed and wet strength tests performed.

TABLE 1 Reacted With Free Aldehyde mg. NH OH'HCl per content W.S. Fraction 2 g. modified gum m moles/I00 g. lb./15 mm. 11 5.3 9.8 2.1 Ill 1 L2 9.1 2.0 W 18.5 7.0 1.6

These results are plotted for curve C, and similar results are shown schematically for Gums A, B, and D treated in similar manner with hydroxylamine hydrochloride. Clearly for any given COOH content as the CH content falls, so do the wet strength properties. Conversely, it may be seen that if a particular Cl-IO content is selected, say 20 m moles/ 100 g. gum, the wet strength of a pulp may be predicted for any given COOH content. For example an additive containing 20 m moles CH0, and 40 m moles COOl-I would produce a paper wet strength of 1.2 lbs. If the COOH is reduced to about 28 m moles the wet strength increases to about 2.2 lbs., further reduction of the COOH to about 18 m moles increases the wet strength to about 3.2 lbs., and so on. It may be further concluded that a given wet strength may be obtained with oxidized gums which have been modified to various total extents or with differing aldehyde/carboxyl ratios. For example, it may be predicted that when the gum of Example 1 is added to bleached kraft pulp, a wet strength of approximately 3.1 lbs. should be achieved or an increase of slightly more than 500 percent, and with the gum of Example 2 a wet strength of 2.6 lbs. shouldbe achieved. Example 7 shows an actual increase of 440 percent when using the product of Example 1. Aspr'eviously indicated the gum of Example 17, which is .not oxidized according to the present invention, should produce a wet strength in excess of 4.0 lbs. whereas in fact this gum only produces a wet strength of 2.3 lbs. and hence it may be said that enzymatic oxidation is not as effective to produce wet strength additives as the acid-dichromate system of the present invention. In practice, the modified gum having the desired aldehyde/carboxyl ratio would be produced by the method affording the maximum economies consistent with obtaining the desired wet strength characteristics and the availability of raw materials.

Throughout the present specification it has been stressed that improvements in the wet strength characteristics of paper are desirable for certain purposes, but it must also be stressed that heretofore such improvements have usually been associated with a deterioration of the repulping properties of the paper. In any paper mill operation significant quantities of scrap or reject material are produced and for efficient operations it is of fundamental importance that this scrap material is repulped and converted to a usable product. If the wet strength additive detracts from the repulping properties, expensive retreatments may become necessary and thus the commercial advantage of a cheap wet strength additive may be lost.

It has been found that when the pH of a pulp containing the novel additive of the present invention is raised to about 10 the wet strength is lost. Similarly, if a formed sheet is treated at a pH of 10, it rapidly disintegrates. A pH of about 9 is sufficient to cause disintegration if accompanied by some beating action. This means that there is easy recovery and repulping of the scrap or reject material in spite of the high wet strength of a pulp which includes the additive of this invention.

I claim:

1. A composition of matter selected from the group consisting of guar gum, locust bean gum, damson gum,

tamarind gum and laminaran having the formula:

ll wherein n is an integer greater than I, each X is selected from primary alcohol groups, and oxidized primary alcohol groups, provided that at least some of said X groups are aldehyde groups, and others of said X groups are carboxylic groups, the ratio of aldehyde groups to carboxylic groups being at least 0.9 l and Y is selected from the group consisting of hydroxyl and keto.

2. An oxidized non-cellulosic polysaccharide selected from the group consisting of guar gum, locust bean gum, damson gum, tamarind gum and laminaran having the formula:

H Y C H2 

2. An oxidized non-cellulosic polysaccharide selected from the group consisting of guar gum, locust bean gum, damson gum, tamarind gum and laminaran having the formula:
 3. An oxidized non-cellulosic polysaccharide selected from the group consisting of guar gum, locust bean gum, damson gum, tamarind gum and laminaran, having the formula: 